title: Initial response and cellular protection through the Keap1/Nrf2 system during the exposure of primary mouse hepatocytes to 1,2-naphthoquinone.
abstract: Quinones are reactive chemical species that cause cellular damage by modifying protein thiols and/or catalyzing the reduction of oxygen to reactive oxygen species, thereby promoting oxidative stress. Transcription factor Nrf2 plays a crucial role in cellular defense against electrophilic modification and oxidative stress. In studies using 1,2-naphthoquinone (1,2-NQ) as a model quinone, we found that Keap1, the negative regulator of Nrf2, was readily arylated at its reactive thiols by 1,2-NQ. Exposure of primary mouse hepatocytes to 1,2-NQ resulted in the activation of Nrf2 and the upregulation of some of Nrf2's downstream genes. This interaction was further investigated in hepatocytes from Nrf2 knockout mice in which the proteins responsible for the metabolism and excretion of 1,2-NQ are minimally expressed. The chemical modification of cellular proteins by 1,2-NQ was enhanced by Nrf2 deletion, resulting in increased toxicity. However, deletion of the negative regulatory protein, Keap1, drastically reduced the covalent binding by 1,2-NQ and its cellular toxicity. Experiments with chemicals that inhibit the biotransformation and extracellular excretion of 1,2-NQ suggest that 1,2-NQ undergoes detoxification and excretion into the extracellular space predominantly by two-electron reduction and subsequent glucuronidation by NAD(P)H:quinone oxidoreductase 1 and uridine 5'-diphosphate-glucuronosyltransferases, followed by multidrug resistance-associated protein-dependent excretion. These findings suggest that the Keap1/Nrf2 system is essential for the prevention of cell damage resulting from exposure to 1,2-NQ.
authors.affiliation: Doctoral Programs in Medical Sciences, Graduate School of Comprehensive Human Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Miura
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Shinkai
authors.forename: Hai-Yan
authors.initials: HY
authors.lastname: Jiang
authors.forename: Noriko
authors.initials: N
authors.lastname: Iwamoto
authors.forename: Daigo
authors.initials: D
authors.lastname: Sumi
authors.forename: Keiko
authors.initials: K
authors.lastname: Taguchi
authors.forename: Masayuki
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Hideto
authors.initials: H
authors.lastname: Jinno
authors.forename: Toshiko
authors.initials: T
authors.lastname: Tanaka-Kagawa
authors.forename: Arthur K
authors.initials: AK
authors.lastname: Cho
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Kumagai
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D000072019:Kelch-Like ECH-Associated Protein 1; D051379:Mice; D018345:Mice, Knockout; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism*; D009285:Naphthoquinones / Q000737:chemistry / Q000633:toxicity*; D010455:Peptides / Q000737:chemistry; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; D009285:Naphthoquinones; C495636:Nfe2l2 protein, mouse; D010455:Peptides; C040756:1,2-naphthoquinone; D016660:NAD(P)H Dehydrogenase (Quinone); C491732:Nqo1 protein, mouse; D014453:Glucuronosyltransferase